1. Field of the Invention:
The invention in general relates to integrated circuit devices, and more specifically to an integrated circuit device particularly well adapted for use in the sonar field for forming beams.
2. Description of the Prior Art
Various acoustic imaging and/or sensing systems require the formation of one or more beams. For example, an underwater detection system may employ a plurality of hydrophone sensors which, together with signal processing circuitry, form multiple simultaneous beams to search large volumes rapidly.
In order to steer or form a beam in a particular direction, appropriate electrical delays must be provided for the output of each hydrophone sensor in such a way as to cancel propagation delay of a wave front incident on the array of hydrophone sensors, from a particular direction. Where space is not at a premium, a typical beamformer circuit may include relatively large passive delay lines or phase shifting networks connected to the sensors for supplying the necessary delays. There are however, systems in which the total volume which can be used for acoustic detection apparatus, is limited. One such example is an acoustic homing torpedo which includes a sensor array and wherein it is desired to form a beam in a particular direction, and/or form multiple beams which may have the capability of being steered.
Accordingly, for volume limited applications, the well-known charge-coupled device (CCD) has been suggested as an integrated circuit substitute for the delay line normally used in beam forming applications.
In one proposed system, a plurality of standard length CCD's is provided, each one connected to a respective sensor element. Clocking signals provided to the CCD's step an injected signal along the lengths thereof. In order to achieve different delay times, however, a different stepping frequency must be used for each CCD, necessitating a complicated clock generator system.
In another proposed system a single clock generator provides identical signals to a plurality of CCD's, each connected to a respective sensor element, with the variable delay times being accomplished by tapping in to the CCD delay line at appropriate positions. This type of arrangement requires separate output circuits at each of the tap positions, and with a multiplicity of beams to be formed, the arrangement requires a great deal of interconnects between the CCD's and a summing amplifier and it has been found that the dynamic range of such device is somewhat limited.
One CCD arrangement, such as described on page 200 of the 1976 IEEE International Solid State Circuits Conference Digest of Technical Papers, forms an electronic lens by connecting the outputs of transducer elements of an array to a plurality of CCD devices of varying length. The arrangement uses two groups of cascaded CCD's with the second group requiring a different clock frequency.